The subject matter of the present invention relates generally to dewatering apparatus for papermaking machines and in particular to suction box apparatus, including a composite suction box cover having cover elements mounted in slots on cross braces. The cross braces which may be of metal extend across such cover elements and longitudinally of the porous conveyor belt conveying the paper web from which water is to be removed by the suction box or other dewatering apparatus. The composite suction box cover is preferably formed by cover strips of ceramic material bonded to fiber-reinforced plastic support members extending beneath such ceramic strips. The support members are provided with mounting projections which engage mounting slots in the cross braces for releasably mounting such cover strips on such cross braces without the use of threaded fasteners such as screws or bolts and without the need for welding or other time consuming and expensive fastening means.
The drainage apparatus of the present invention is especially useful in the manufacture of paper, pulp stock and nonwoven fabrics for the removal of water from the material being manufactured.
Previously it has been proposed in U.S. Pat. No. 4,140,573 of Johnson, issued Feb. 20, 1979, to provide a suction box apparatus, including a suction box cover formed by a plurality of cover elements or blades mounted on support rails of T-shaped cross section called "T-bars" which extend across the width of the conveyor belt on which the paper stock is transported. These T-bar support members are conventionally fastened to cross brace members by welding or by bolts or other mechanical fasteners which is extremely expensive and time consuming process. In addition, in the case of threaded mechanical fasteners, there is a continued maintenance problem because such fasteners can loosen and fall into the papermaking machinery and onto the conveyor belt, "wire" or fabric, thereby damaging the machinery or conveyor belt. When the T-bar support members are welded to the cross braces, this overcomes the problem of loosening bolts and damage to the papermaking machine but the fastening is extremely expensive and time-consuming. The suction box cover apparatus of the present invention avoids the need for welding or threaded fasteners by using metal cross braces which are slotted with mounting slots to engage mounting projections on the bottom of support members of fiber-reinforced plastic material to which the cover strips of ceramic material are bonded. This overcomes the above-mentioned problems and has the added advantage that allows the cover elements to be easily inserted and removed in the case of damage or replacement of the cover elements for other reasons. The cross braces are made in a simple and inexpensive manner by machining metal bar stock rather than requiring the bracing to be made by casting, and thereby allows a greater flexibility in the design of the suction box cover to accommodate changes in the width of the cover elements and the drainage slot spacing between elements which varies, depending upon many factors, including the position of the suction box in the papermaking machine and the vacuum pressure within such suction box.
In U.S. Pat. No. 4,334,958 of Baluha et al issued June 15, 1982, it has been previously proposed to provide a suction box cover element or a dewatering foil, including a wear insert of ceramic material bonded to a fiber reinforced plastic base support member to provide a cover element which is secured by a dovetail tongue and groove connection on the bottom of the support member to a lower section or intermediate support member of plastic material which is mounted on a T-bar bracket attached by bolts to the top of a frame member. However, this extremely complicated device differs from that of the present invention in that it employs bolts to fasten the T-bar brackets which can loosen and fall out to damage the conveyor wire and does not provide slotted cross braces having mounting slots in which the cover elements are secured by mounting projections on the bottom of such cover elements.
Suction box covers have previously been provided with metal cross braces as shown in U.S. Pat. No. 1,657,509 of Latham, issued Jan. 31, 1928, and U.S. Pat. No. 1,696,917 of Lewis, issued Jan. 1, 1929, which show cover elements of wood attached to metal bars supported on cross braces or bridge members. Also, U.S. Pat. No. 3,708,390 of Krake, issued Jan. 2, 1973, discloses a felt dewatering apparatus, including a suction box employing plastic cover elements attached to J-shaped metal supports supported on a metal plate. However, metal cross braces have not been employed to mount suction box cover elements directly thereon by means of mounting slots provided in such cross braces in the manner of the present invention.
While the preferred embodiments of the present invention are hereafter described with respect to a suction box cover, the present invention applies to other types of drainage apparatus used in papermaking machines, including dewatering devices which engage the felt conveyor belt in the press section of such machines as well as foil type water removal devices in the sheet forming section which produce a vacuum pressure by the foil action of the conveyor belt as it passes over the contacting leading edge and the diverging trailing edge of such foils and thus do not require an external source of vacuum pressure in the manner of suction boxes. In addition, it should be noted that the drainage box covers can have their conveyor contacting surface either flat or of a convexly curved shape. Also, the cover strips of ceramic material can be of varying widths and spacing between adjacent cover strips to provide drainage slots can be of varying widths.